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HOMEOSTASIS. Thermoregulation. Louis Chow. What is it?. Significance?. Enables organisms to explore inhospitable environments. Homeostasis. The ability of the body to maintain a constant internal environment despite fluctuations in both the body’s activities and the external environment

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Louis Chow

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Louis Chow

What is it?


Enables organisms to explore inhospitable environments


  • The ability of the body to maintain a constant internal environment despite fluctuations in both the body’s activities and the external environment

  • Consists of specific values which are considered as normal

Negative Feedback Mechanism...

Negative feedback mechanism

  • Receptors detects a stimulus (external or internal change).

  • Communication between the receptor and the effector(through a control centre).

  • Effector brings about the response to restore balance.

  • When the response is enough to return the body back to its normal state, the receptor is turned off.

Why control body temperature?

  • Independence from changing environments

  • Affects the rate of metabolic reactions

  • Sensitivity of enzymes



  • Fish, amphibians, reptiles etc.

  • Body temperature is greatly dependent on the external temperature

  • Variable metabolic rate

  • Activity levels determined by external environment

Behavioral responses

  • Voluntary responses

  • Temperature too cold: cuddling, put on more clothes, eating, more muscular activities, move closer to heat sources, e.g the Sun

  • Temperature too hot: Less clothing, cool drinks, find shades, body orientation



  • Mammals and birds

  • Body temperature is less dependent on the external temperature

  • High metabolic rate

  • Possess thermoregulating mechanisms

Physiological adaptions

  • controlled by the thermoregulatory centre in the hypothalamus.

  • Receptors in the hypothalamus itself(blood temperature, the core temperature)

  • Skin receptors (the external temperature)

  • Also controlled by the cerebral cortex -- Voluntary actions

Heat gain vs heat loss

Heat Exchange between organisms and their surroundings:

Core temperature and skin temperature

  • http://www.youtube.com/watch?v=Vlp_NHuC0rw




Increase heat gain

decrease heat loss

  • decrease heat gain

  • Increase heat loss

Pilorelaxation and Piloerection

Relaxation of erector muscle Contraction of erector muscle

Vasodilation and Vasoconstriction



Skin arterioles constrict

Sphincter muscles contract

Shunt vessels dilate

Blood flow to skin capillaries decreased

  • Skin arterioles dilate

  • Sphincter muscles relax

  • Shunt vessels constrict

  • Blood flow to skin capillaries increased

Sweat production



Inhibition of sweat glands

Decreased sweat production

  • Activation of sweat glands

  • Increased sweat production

Extreme temperatures



Core temperature higher than 38.5 degrees Celsius

Adverse effects by drugs

Heat stroke

Dizziness, confusion

  • Core temperature falls below 35 degrees Celsius

  • Enhanced by alcoholic effects

  • Amnesia, death

Preventing hypothermia

  • Wear more clothes!!

  • Avoid diving in cold water

  • Go closer to heat sources

Preventing hyperthermia

  • Find shades

  • Avoid excess exercise

What might come in the exam..

  • Where is the best place to take a temperature of a person?

  • Define evaporative heat loss.

  • Describe and explain a way of losing heat.


Thank you!

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